Copper in topsoils

Summary

Copper (Cu) distribution in soil is influenced by climatic, geological and pedological factors. Apart from geological sources and industrial pollution, other anthropogenic sources, related to the agricultural activity, may increase copper levels in soils, especially in permanent crops such as olive groves and vineyards. This study uses 21,682 soil samples from the LUCAS topsoil survey to investigate copper distribution in the soils of 25 European Union (EU) Member States.

Generalized Linear Models (GLM) were used to investigate the factors driving copper distribution in EU soils. Regression analysis shows the importance of topsoil properties, land cover and climate in estimating Cu concentration. Meanwhile, a copper regression model confirms our hypothesis that different agricultural management practices have a relevant influence on Cu concentration. Besides the traditional use of copper as a fungicide for treatments in several permanent crops, the combined effect of soil properties such as high pH, soil organic carbon and clay, with humid and wet climatic conditions favours copper accumulation in soils ofvineyards and tree crops. Compared to the overall average Cu concentration of 16.85 mg kg-1, vineyards have the highest mean soil Cu concentration (49.26 mg kg-1) of all land use categories, followed by olive groves and orchards.

Gaussian Process Regression (GPR) combined with kriging were used to map copper concentration in topsoils and to evidence the presence of outliers. GPR proved to be performant in predicting Cu concentration, especially in combination with kriging, accounting for 66% of Cu deviance. The derived maps are novel as they include information about the importance of topsoil properties in the copper mapping process, thus improving its accuracy. Both models highlight the influence of land management practices in copper concentration and the strong correlation between topsoil copper and vineyards.

The LUCAS physical and chemical attributes allow the assessment of additional factors influencing Cu retention in soils, namely soil pH and soil texture. Even if the Cu accumulation is correlated mostly to soil properties, environmental factors such as climate (e.g., summer rainfall) and lithology also plays a relevant role, at least in some parts of the EU.

Potential Sources of Anthropogenic Copper Inputs to European Agricultural Soils

Anthropogenic sources of diffuse copper contamination include fungicidal treatments, liquid manure (mainly from pigs), sewage sludge, atmospheric deposition, mining activities, local industrial contamination and particles from car brakes. Sales of fungicides in the EU are around 158,000 tonnes annually, a large proportion of which are copper based and used extensively in vineyards and orchards. Around 10 million tonnes of sewage sludge is treated annually in the EU, and 40% of this (which has a high copper content) is used as fertilizer in agriculture. In the EU, 150 million pigs consume more than 6.2 million tonnes of copper through additives in their feed, and most of their liquid manure ends up in agricultural soil. These three sources (sales of fungicides, sewage sludge and copper consumption for pigs feed) depend much on local traditional farming practices. Recent research towards replacing copper spraying in vineyards and policy developments on applying sewage and controlling the feed given to pigs are expected to reduce copper accumulation in agricultural soil. A recent published article describes in detail those antropogenic sources of copper concentration.

Data

The result of the regression and interpolation model is the Map of topsoil Copper concentration (mg Kg-1). The spatial interpolated data (as seen in the figure below) are available for public user.

The aggregated data (mean per region NUTS2) both for all land uses and only for agricultural lands are also available. The aggregagted data are calculated based on the raw LUCAS data.